1. Field of the Invention
The present invention relates to a semiconductor device including a semiconductor film having a crystal structure and particularly to a semiconductor device including a crystalline semiconductor film raised on an insulating surface and a field-effect transistor such as a thin film transistor and/or a bipolar transistor especially. In addition, the present invention relates to a semiconductor device producing system for crystallizing a semiconductor film by using laser light and for activating a semiconductor film after ion implantation.
2. Description of the Related Art
A technology has been known for crystallizing an amorphous semiconductor film over a substrate of, for example, glass through laser processing. The laser processing may be a technology for re-crystallizing a damaged layer or an amorphous layer on a semiconductor substrate or a semiconductor film, a technology for crystallizing an amorphous semiconductor film on an insulating surface, or a technology for improving the crystallinity of a semiconductor film having a crystal structure (crystalline semiconductor film). A laser oscillating device used for the laser processing generally uses gaseous laser such as excimer laser or solid laser such as YAG laser.
Laser beam is used because an area absorbing energy from irradiated laser beam can be. heated selectively in comparison with heat processing using radiant heating or conductive heating. For example, laser processing using excimer laser oscillating device for oscillating ultra violet light having a wave length equal to or less than 400 nm heats a semiconductor film selectively and locally. Then, crystallization and/or activation processing can be performed on the semiconductor film by hardly damaging the glass substrate thermally.
JP Laid-Open 62-104117 (page 92) discloses laser processing in which an amorphous semiconductor film is crystallized without melting the semiconductor film completely by adopting rapid scanning using laser of (beam spot diameter×5000)/second or more. U.S. Pat. No. 4,330,363 (FIG. 4) discloses laser processing in which an extended laser beam is irradiated to an island-shaped semiconductor area to form a single crystalline area essentially. Alternatively, JP Laid-Open 8-195357 (Pages 3 to 4 and FIGS. 1 to 5) discloses a method in which a beam to be irradiated is processed linearly by an optical system such as a laser processing apparatus.
Furthermore, for example, JP Laid-Open 2001-144027 (Page 4) discloses a crystallization technology using a solid laser oscillating device with, for example, Nd: YVO4 laser. According to the technology, a second harmonic of a laser beam projected from the solid laser oscillating device is used such that a crystalline film having a larger crystal grain size than the conventional size can be obtained to be applied for a thin. film transistor (called “TFT” hereinafter).
The application to a thin film transistor (called “TFT” hereinafter) in the crystallization technology using the solid laser oscillating device is reported in A. Hara, F. Takeuchi, M. Takei, K. Yoshino, K. Suga and N. Sasaki, “Ultra-high Performance Poly-Si TFT on a Glass by a Stable Scanning CW Laser Lateral Crystallization”, AMLCD ′ 01 Tech. Dig., 2001, pp. 227-230. According to the result described in the document, a second harmonic wave of a diode-excited solid continuous wave laser (YVO4) is used to crystallize an amorphous silicon film to be used for producing a TFT.
Conventionally, improvement in TFT characteristics may have required improvement in crystallinity of the active layer (which is a semiconductor film including regions and/or a semiconductor film having source or drain regions, here).
Forming a single crystalline semiconductor on an insulating surface has been attempted for a long time. A technology called Graphoepitaxy was designed as a more active attempt. According to Graphoepitaxy, grade changes are formed on a surface of a quartz substrate. Then, an amorphous film or a polycrystalline semiconductor film is formed thereon. By heating it by using a laser beam or a heater, an epitaxial growing layer is formed by having the grade change on the quartz substrate as a core. The technology is disclosed in J. Vac. Sci. Technol., “Grapho-epitaxy of silicon on fused silica using surface micropatterns and laser crystallization”, 16(6), 1979, pp. 1640-1643, for example.
In addition, M. W. Geis, et al., “CRYSTALLINE SILICON ON INSULATORS BY GRAPHOEPITAXY” Technical Digest of International Electron Devices Meeting, 1979, pp. 210 discloses a semiconductor film crystallization technology called graphoepitaxy. The technology attempts epi-raising of a semiconductor film by inducing grade changes on a surface of an artificial amorphous substrate. In the graphoepitaxy disclosed in the document, grade changes are provided on a surface of an insulating film, and processing including heating or irradiating laser light is performed on a semiconductor film on the insulating film. Thus, crystal of the semiconductor film is epitaxially raised.
However, in order to form a semiconductor film having good crystallinity with fewer defects and/or crystal grain boundaries and with uniform alignment, a semiconductor is conventionally and mainly heated to a higher temperature to be melted and then is crystallized. This is known as a band melting method.
According to the publicly-known graphoepitaxy technology, grade changes in a primary layer is used. Thus, crystal grows along the grade changes. As a result, the grade changes remain on the surface of the formed single crystalline semiconductor film disadvantageously. Furthermore, a single crystalline semiconductor film cannot be formed by using the graphoepitaxy on a large glass substrate having smaller distortion points.
In all of the cases, a crystalline semiconductor film having fewer defects cannot be formed due to the volume shrinkage of the semiconductor, thermal stresses against the base, grating mismatch and so on caused by crystallization. Furthermore, distortions are accumulated. Thus, an area causing defects cannot be positionally controlled so as to position in the other area than element forming areas. Accordingly, without bonded SOI (silicon on insulator), a crystalline semiconductor film on an insulating surface cannot obtain the same quality as that of a MOS transistor provided on a single crystalline semiconductor.